The present invention relates in general to a control apparatus for an electric vehicle, such as an electric railcar and an electric locomotive; and more particularly, the invention relates to an electric vehicle control apparatus which prevents deterioration in riding comfort in the electric vehicle by decreasing the braking force at a prescribed rate of change when stopping the vehicle, and establishes a timing for release of the electric braking such that the electric vehicle stops completely, based on the rotational speed and rotational deceleration of the electric motor of the electric vehicle.
Conventionally, in electric vehicles, it is very common to perform brake control by using both electric brakes and pneumatic brakes, and, in particular, the braking is carried out using only pneumatic brakes from a speed below a specific speed up to a complete stop. This is due to the fact that, since relatively inexpensive pulse generators having a small number of pulses per revolution are being used for detecting the rotational speed of the motor, it is not possible to obtain a speed detection accuracy such that the zero speed point can be determined in a range of an extremely low speed just before stopping; and, hence, while the braking force can not be sufficiently controlled in the range of low speed by the electric brakes, it is possible to surely control the braking force up to stopping when the pneumatic brakes are used. In this case, changeover from electric braking to pneumatic braking is carried out while controlling the brakes so as to make the sum of the two braking forces constant, and an almost constant deceleration force is maintained up to stopping in this way.
JP A 7-7806, which is directed to a xe2x80x9cRegenerative braking control method for electric vehiclesxe2x80x9d, discloses a control method in which, when an actual regenerative braking force is applied to pneumatic braking equipment, an attempt is made to achieve smoothness in operation at the time of changing over from the regenerative braking to pneumatic braking by multiplying the actual regenerative braking force by a coefficient, while taking into consideration the delay in the operation of the pneumatic brakes, over the entire range of the braking force command, comprising brake step and variable load conditions.
Further, regarding a method of controlling electric brakes, JP A 11-234804, which is directed to an xe2x80x9cElectric Vehicle Reverse Phase Electric Brake Control Method and Equipmentxe2x80x9d, describes a method of detecting zero speed in reverse phase electric braking by detecting that the speed of the electric vehicle has become zero during braking using reverse phase electric braking, while obtaining the braking force by changing over from braking the forward movement to applying a reverse direction driving force as the speed gets reduced.
Although the xe2x80x9cRegenerative braking control method for electric vehiclesxe2x80x9d disclosed in JP A 7-7806 is effective for preventing generation of a shock at the time of changing over from regenerative braking to pneumatic braking, there is the problem that the actual braking force in pneumatic braking can easily change from the command value of braking force due to various conditions, such as the weather, etc., and the ease of carrying out the braking operation becomes poor after changing over from regenerative braking to pneumatic braking. Also, it is desirable for the frequency of use of pneumatic braking to be reduced as much as possible, considering the noise which is generated due to brake screeching at the time of applying the pneumatic brake in the low speed range, and the cost of replacement work of the brake shoes (brake pads).
Further, in the xe2x80x9cElectric Vehicle Reverse Phase Electric Brake Control Method and Equipmentxe2x80x9d disclosed in JP A 11-234804, there is no clear description regarding the method of decreasing the torque, which is considered to have a large effect on the riding comfort during stopping.
An object of the present invention is to provide a control apparatus for an electric vehicle which is stopped by electric braking, which control apparatus can simultaneously achieve reliable braking and good riding comfort particularly by determining a suitable timing for release of the electric braking such that the electric vehicle stops completely and the braking force is decreased at a specific rate of change to stop the electric vehicle.
The shock which is generated due to sudden changes in braking force is reduced by decreasing the braking force just before stopping at a prescribed or specific rate of change, and the timing for release of the electric brake so as to stop completely is derived on the basis of the rotational speed and rotational deceleration of the electric motor, considering the rate of change of the reduction of the braking force and the delay in detecting the speed.